The present invention relates to improvements in an anti-creep control apparatus of an automatic transmission of a vehicle.
Various anti-creep control apparatus of an automatic transmission have been proposed in order to prevent a so-called creep phenomenon that part of engine power is transmitted to an output shaft of the automatic transmission due to the rotation of the torque converter and to decrease the vibration and the energy consumption during idling of the vehicle. Japanese Patent Provisional Publication No. 60-220260 discloses a typical anti-creep control apparatus for an automatic transmission, where a friction element installed in a motive power transmitting system is controlled such that a difference between input and output shaft rotation speeds of a torque converter installed between an engine and the automatic transmission is set at a predetermined value necessary to avoid the creep of the vehicle when the automatic transmission is set in a drive range and when the engine is driven in an idling speed. On the other hand, Japanese Patent Provisional Publication No. 5-157173 discloses another typical anti-creep control apparatus of an automatic transmission, which apparatus is arranged to quickly engage a forward clutch if a driver intends to quickly start the vehicle and to slowly engage the forward clutch so as to decrease a shock in the clutch releasing operation if a driver does not intend to quickly start the vehicle.
The former conventional anti-creep control apparatus is arranged to execute the anti-creep control during a time period from the time when the shift position of the automatic transmission is changed from N-range to D-range to the time when the acceleration pedal is depressed. Therefore, just after the depression of the acceleration pedal, the forward clutch is smoothly engaged while the clutch of the automatic transmission is slipped according to the increase of the engine rotation speed. In this case, it becomes possible to ensure a smooth starting without a shock although the responsibility of the vehicle starting is degraded since the rising of output shaft torque is delayed. During this time period, the clutch is slipped while receiving large torque. Therefore, the clutch generates large amount of heat and degrades the durability thereof. On the other hand, the later conventional anti-creep control apparatus is arranged to quickly increase the hydraulic pressure of the forward clutch when intended to start the vehicle. Although the forward clutch is quickly engaged by this quick decrease of the output shaft rotation speed, the quick engagement of the forward clutch generates a torque shock impressing discomfort to a driver.